In no way is the "Bitcoin's bullet proof BTC/blockchain linkage" broken. The coins aren't actually moved to the other chain, they are held on the mainchain like gold in a vault and a representation which is NOT BTC and can't be spent at coinbase for example, appears on the sidechain.
There is no way sidechains break the 21 million scarcity limit of real BTC. And anything that a sidechain could do to "dilute" the space (that is by creating a new token type) can be done with an altcoin today, and that has gotten nowhere. Any "betrayal" of the BTC "brand" that can be done with sidechains can equivalently be done much more easily (and with the same brand damage) with centralized solutions. We've seen it over and over again; Gox ponzi didn't kill BTC, and SCponzi won't either. But the risk of SCponzi will certainly make the mainchain the preferred place to hold and make large transfers. Sidechains will make Bitcoin the preferred long term store of value, because tremendous utility is just a chain transfer away.
And how is Gox going to go Ponzi when the GoxBTC and GoxUSD on its sidechain must match the BTC "locked" on the mainchain and the USD in their bank accounts (which can be audited)?
If a multi-token sidechain is created with scBTC and inflata-Coin-to-make-devs-rich, what do you think people will do? Probably not even touch the sidechain. But assuming they do, they will hold the scBTC and when they need to "use" the sidechain features the require inflata-coin, they'll buy the inflata-coin moments before spending it.
But without sidechains you really do risk a new token that comes along and takes massive market share. We as a society are not ready to put stocks, mortgages, etc on a blockchain (because why have the risk of a new tech coupled with the return of an old stock). But someday we WILL be. And when we are, what's going to be the preferred payment? Old stodgy BTC that you have to sign up for exchanges, do AML, etc to access real markets, or tradecoin which can be tranformed into GOOG 5 seconds after receipt? There's a REASON gold shot up when ETFs appeared -- its called access to markets.
What about the IOT (internet of things) token? 20 years from now, items in your house might be doing 500 txns per day for a total of < $5 automatically on your behalf... Sidechains allow BTC to scale beyond our wildest dreams to applications we can't even consider.
You are like the guy who said there's only use for 5 computers in the world.
You should instead consider that the biggest risk to BTC right now is the sidechain-altcoin that Blockstream so "kindly" offered to build instead of integrating these technologies directly into BTC. That altcoin has the potential to leave BTC in the backwaters of digital currencies (except that I believe in the core devs in Blockstream to move the tech over).
Ok, that's probably the end of my rant... but my subsequent silence does not mean that you are right :-). Honestly, I miss the great insights you guys (and mostly cypherdoc) provide about the larger world economic picture on this thread and hope that we can eventually get back to it! But I'll tell you this; I'm a technologist and I've skipped from one newly breaking technology to the next for my entire career in startups; gaming, telecom in 1995-2000, storage, wireless, OSHW, bitcoin. I'm telling you if sidechains CAN be done (honestly I haven't really verified the gory details of the automated 2-way peg myself) they WILL eventually be the dominant coin. I proposed them in early 2012 (the concept not the mechanism)... but don't worry to much, BTC will not die; it'll be the Rolls Royce with a valuation above what we have today, while the sidechain-enabled coin takes 99% of the market.
EDIT: tl;dr. Bitcoin is the zerg. It will take over everything thru sidechains.
That's a really persuasive argument from someone I respect.
The other way to question this though is that somehow btc units are fed through the peg and through some magic stocks, bonds , smart contracts, altcoins, etc come out the other side and somehow this is not inflationary? What if it just breaks the entire system?